Preconception Health: What Actually Makes a Difference

The honest picture, with numbers

Preconception health is a crowded market. Supplement stacks, fertility diets, cleanses, apps that promise to find your one perfect day — most of it has either no evidence behind it or evidence too weak to act on. The list of things with real supporting data is short. That is good news, not bad: it means there are not ninety-nine things you have been failing to do.

Start with the baseline you are working from. NICE guideline NG257 reproduces cumulative conception data for couples having vaginal intercourse roughly twice a week without contraception: 92% of women aged 19 to 26 conceive within 12 cycles and 98% within 24; 87% and 95% at 27 to 29; 86% and 94% at 30 to 34; and 82% and 90% at 35 to 39. Most people conceive without changing anything. Preconception health is about reducing risk and preparing for a pregnancy, not about earning one.

The intervention with the strongest evidence is also the cheapest. Cochrane's review of periconceptional folate supplementation, covering five trials and 6,708 births, found a risk ratio of 0.31 (95% CI 0.17 to 0.58) for neural tube defects — roughly a 70% reduction. It works in the first weeks of pregnancy, often before you know you are pregnant, which is exactly why it belongs in the preconception period rather than the antenatal one.

What actually makes a difference

Folic acid, started before you conceive

The NHS recommends 400 micrograms of folic acid every day, ideally from three months before conception and through the first 12 weeks of pregnancy. A higher 5 mg prescribed dose is recommended if you or the baby's other biological parent has a neural tube defect or a relative with one, if you have had a previous affected pregnancy, if you have diabetes, if you have a blood condition such as sickle cell anaemia or thalassaemia, or if you take medicine for epilepsy or HIV. ACOG's equivalent advice is at least 400 micrograms starting at least a month before pregnancy, with 4 mg — ten times the usual amount — for those who have previously had a child with a neural tube defect.

Vitamin D

The NHS advises 10 micrograms (400 IU) of vitamin D daily from early October to late March, and all year round if you usually cover most of your skin outdoors, spend a lot of time indoors, or have black or brown skin. Do not take more than 100 micrograms a day.

Not taking certain things

The NHS is specific: do not take cod liver oil or supplements containing vitamin A (retinol) when pregnant, because too much vitamin A can harm fetal development. Check the label of any multivitamin you are already using rather than assuming a product marketed at women is safe in pregnancy.

Smoking, including passive smoking

NG257 states that smoking is likely to reduce fertility in women, and that passive smoking is likely to affect the chance of conceiving. ASRM's committee opinion puts the odds ratio for infertility in smokers at 1.60 (95% CI 1.34 to 1.91), and the odds of taking more than 12 months to conceive at 1.42 (95% CI 1.27 to 1.58). This is one of the few modifiable factors where the effect size is both real and reversible.

Alcohol

NG257 advises that drinking no more than 1 or 2 units once or twice a week, and avoiding episodes of intoxication, reduces the risk of harming a developing fetus, and notes that under the Chief Medical Officer's guidelines the safest approach is to avoid alcohol altogether. For a male partner, NICE says drinking within 14 units a week spread across several days is unlikely to affect semen quality.

Weight, stated as the guideline states it

NG257 says a BMI of 30 or over is associated with taking longer to conceive, and that if you are not ovulating, losing weight is likely to increase the chance of conception. It also says a group programme involving exercise and dietary advice leads to more pregnancies than weight-loss advice alone. Separately, for a BMI under 18.5 with irregular or absent periods, increasing body weight is likely to improve the chance of conception.

How often, rather than exactly when

NICE recommends vaginal intercourse every 2 to 3 days to optimise the chance of pregnancy. ASRM notes the highest pregnancy rates come from intercourse every 1 to 2 days during the fertile window — the six days ending on the day of ovulation. Both approaches beat trying to hit a single calculated day, and the every-2-to-3-days version does not require you to know when you ovulate.

The checks worth doing before you are pregnant

NG257 recommends offering rubella testing to anyone concerned about fertility who is unsure whether they were vaccinated, and vaccination if susceptible — with advice not to conceive for at least a month afterwards. It also recommends asking about the timing and result of your most recent cervical screening so treatment is not delayed later, and chlamydia screening before any uterine instrumentation. The NHS adds MMR vaccination and STI testing to the pre-pregnancy list.

Your medicine list

NG257 asks clinicians to check for prescription drugs such as GLP-1 agonists, testosterone-replacement therapy and finasteride; over-the-counter products including NSAIDs and vaginal lubricants; and recreational drugs including anabolic steroids and cannabis. The NHS is equally clear in the other direction: do not stop taking any prescribed medicine until you have talked to your GP or specialist.

What the evidence does not support

Three absences are worth naming, because they are where most of the guilt lives.

• Caffeine. NICE states there is no consistent evidence of an association between caffeinated drinks — tea, coffee, energy drinks, colas — and fertility problems.
• Complementary therapies. NICE states their effectiveness for fertility problems has not been properly evaluated and that further research is needed before they can be recommended.
• Relaxing. There is no NICE recommendation telling you to reduce stress in order to conceive, because there is no guidance-grade evidence that would support one. When someone tells you it will happen once you stop thinking about it, they are managing their own discomfort.

What to do next

1. Start 400 micrograms of folic acid today if you are not already taking it, and ask a GP whether you meet any of the criteria for the 5 mg dose.
2. Add 10 micrograms of vitamin D and check that nothing you already take contains retinol.
3. Book one pre-pregnancy appointment covering rubella status, cervical screening, long-term conditions and every medicine you take. One appointment resolves most of this list.
4. Settle on intercourse every 2 to 3 days rather than a tracking regime, unless you have a specific reason to track.
5. If either of you smokes, treat that as the priority — it is the modifiable factor with the largest measured effect.
6. Write down the date you started trying. Referral thresholds are counted in months and clinics act on that history.

When to seek help

NG257 recommends offering both partners further clinical assessment and investigation after 1 year of unprotected vaginal intercourse without conception, and referral at first presentation if the woman trying to conceive is 36 or over, or if either partner has a suspected or known clinical cause of infertility or a history of predisposing factors. ACOG advises evaluation after 12 months, or 6 months if you are older than 35.

Go earlier than any of those thresholds if you have irregular or absent periods, known PCOS or endometriosis, previous pelvic infection, previous pelvic or testicular surgery, previous cancer treatment, or recurrent miscarriage. Preconception optimisation is worth doing, but it is not a substitute for investigation, and it should never be the reason a referral is delayed.